The primary goal of this study is to increase the knowledge of treatment methods for patients with pediatric malignancies. The specific aims are the collaboration with other investigators in the Pediatric Oncology Group with entry of pediatric cancer patients on cooperative protocols so that interpretable information can be obtained on a number of patients too large to be followed at any individual institution. This project represents a collaborative effort between the departments of oncology, pediatrics, surgery, radiotherapy, pathology and neurology. The principal studies will involve the evaluation of new TREATMENTS in cancer patients. The biologic, i.e. "non-therapeutic" studies involve analysis of immunologic, biochemical, cytogenetic and other properties of cells which, because they are collected in a systematic fashion in patients treated on protocols can be effectively evaluated for their prognostic significance. A resource laboratory has been established to measure glucocorticoid receptor levels in leukemia cells. The data will be correlated with other marker studies and with clinical response. In addition, new assays to analyze subsequent steps in the action of glucocorticoids, e.g. nuclear translocation of an activated glucocorticoid receptor complex are being developed and will be applied to clinical material where possible. Monoclonal antibodies to antigens which may serve as markers for the classification of non-lymphocytic leukemia are being tested on the leukemia cells from patients on protocol. The development of such a classification system has both basic biologic and clinical implications.